The big factor that you have not brought up is if bitcoin splits into mbtc or something, so that a 1000 dollar bitcoin is now a 1usd mbtc. This would be the smart thing for bitcoin to do in my opinion.
"for Bitcoin to do". Remember Bitcoin can't do anything. The protocol already supports divisions down to 1 sat. When you send "1 BTC" you are actually transfering a value = 100000000. Most clients allow you to show balances in mBTC, uBTC or satoshis.
There will be no formal proclemation. If MtGox tomorrow wanted to change their exchange to show bids, quotes, and balances in mBTC they could and if they don't want to for the next decade nobody can force them.